Re: 2.4.23aa2 (bugfixes and important VM improvements for the highend)

[Magnus Naeslund(t)]

Jamie Lokier wrote:
[snip]
> Any code which is structured like this will break:
>
> 	time_t timeout = time(0) + TIMEOUT_IN_SECONDS;
>
> 	do {
> 		/* Do some stuff which takes a little while. */
> 	} while (time(0) <= timeout);
>
> It goes wrong when time() returns a value that is in the past, and
> then jumps forward to the correct time suddenly.  The timeout of the
> above code is reduced by the size of that jump.  If the jump is larger
> than TIMEOUT_IN_SECONDS, the timeout mechanism is defeated completely.
>
> That sort of code is a prime candidate for the method of using a
> worker thread updating a global variable, so it's really important to
> to take care when using it.

But isn't this kind of code a known buggy way of implementing timeouts?
Shouldn't it be like:

time_t x = time(0);
do {
  ...
} while (time(0) - x >= TIMEOUT_IN_SECONDS);

Ofcourse it can't handle times in the past, but it won't get easily hung 
 with regards to leaps or wraparounds (if used with other functions).

Regards

Magnus


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